Ban, speaking at the start of a special U.N. General Assembly session on the Syrian crisis, condemned the reported massacre at Mazraat al-Qubeir and called again on Assad to immediately implement international mediator Kofi Annan's six-point peace plan.

"Today's news reports of another massacre ... are shocking and sickening," he told the 193-nation assembly. "A village apparently surrounded by Syrian forces. The bodies of innocent civilians lying where they were, shot. Some allegedly burned or slashed with knives."

Ban said U.N. monitors were initially denied access to the site. "They are working now to get to the scene," he said. "And I just learned a few minutes ago that while trying to do so the U.N. monitors were shot at with small arms."

Ban was addressing the General Assembly ahead Annan's expected presentation to the U.N. Security Council on Thursday of a new proposal in a last-ditch effort to rescue his failing peace plan for Syria, where 15 months of violence have brought it to the brink of civil war.

Speaking to the General Assembly after Ban, Annan also condemned the new reported massacre and acknowledged that his peace plan was not working.

The Syrian opposition and Western and Gulf nations seeking the ouster of President Bashar al-Assad increasingly see Annan's six-point peace plan as doomed due to the Syrian government's determination to use military force to crush an increasingly militarized opposition.

By creating such a contact group, envoys said, Annan would also be trying to break the deadlock among the five permanent council members that has pitted veto powers Russia and China against the United States, Britain and France and prevented any meaningful U.N. action on the Syrian conflict, envoys said.

It would attempt to map out a "political transition" for Syria that would lead to Assad stepping aside and the holding of free elections, envoys said. One diplomat said the idea was "vaguely similar" to a political transition deal for Yemen that led to the president's ouster.

The main point of Annan's proposal, they said, is to get Russia to commit to the idea of a Syrian political transition, which remains the thrust of Annan's six-point peace plan, which both the Syrian government and opposition said they accepted earlier this year but have failed to implement.

"We're trying to get the Russians to understand that if they don't give up on Assad, they stand to lose all their interests in Syria if this thing blows up into a major regional war involving Lebanon, Iran, Saudis," a Western diplomat told Reuters. "So far the Russians have not agreed."

Apart from lucrative Russian arms sales to Damascus, Syria hosts Russia's only warm water port outside the former Soviet Union. While Russia has said it is not protecting Assad, it has given no indications that it is ready to abandon him.

Last week, U.S. Ambassador to the United Nations Susan Rice suggested that if Russia continued to prevent the Security Council from putting pressure on Syria, states may have no choice but to consider acting outside the United Nations.

An unnamed diplomat leaked further details of Annan's proposal to Washington Post columnist David Ignatius, who said that if the contact group agreed on a transition deal for Syria, it could mean Russian exile for Assad. The Post article said another option for Assad would be to seek exile in Iran, Syria's other staunch ally.

Annan's peace efforts have failed to halt the violence, as demonstrated by a recent massacre in Houla that led to the deaths of at least 108 men, women and children, most likely by the army and allied militia, according the United Nations.

Opposition members said there was a similar massacre on Wednesday in Hama province, with at least 78 people killed. U.N. monitors were prevented from reaching it, though a pro-government Syrian television station said the unarmed monitoring force did reach the village of Mazraat al-Qubeir.